This invention relates to novel compositions of matter containing optically pure (R)-lomefloxacin. These compositions possess potent activity in treating various infections while avoiding adverse effects associated with racemic lomefloxacin including but not limited to headache, stomach discomfort, gastrointestinal disorders, hypoglycemia, renal and dysfunction, allergic reactions and respiratory distress, and arthropathy, such as cartilage lesions and erosion and abnormalities in bone growth in immature patients. Additionally, these novel compositions of matter containing optically pure (R)-lomefloxacin are useful in treating infection in those patients with impaired renal function. Also disclosed are methods for treating the above-described conditions in a human while avoiding adverse effects that are associated with the racemic mixture of lomefloxacin, by administering the (R)-isomer of lomefloxacin to said human.